Production of pulsatory light



April 11, 1939. c sun-5 2,154,317

PRODUCTION PULSATORY LIGHT Filed Sept. 29, 1938 Fig. I.

i AMPERES Inventor: Ch aunoey G. Suits,

6. AMA by Attornqy.

' UNITED STATES PATENT OFFICE PRODUCTION OF PULSATORY LIGHT Chauncey G. Suits, Schenectady, N. Y., assig'nor to General Electric Company, a corporation oi New York Application September 29, 1938, Serial No. 232,350

3 Claims.

The present invention relates to a novel method and means for producing pulsatory light, that is to say, light which varies "or oscillates intermittently between the condition of relative great luminosity and a condition of lesser luminosity.

Theinvention is considered to be primarily useful in spectacular and display lighting and for signal and warning beacons as at airports and the like.

As will be further explained in the following, pulsatory light production is obtained by the use of a discharge device and supply circuit which are so correlated that the discharge is caused to vary cyclically from a glow to an are state.

The features which I desire to protect herein are pointed out in the appended claims. The invention itself may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 illustrates an appropriate embodiment of the invention and Figs. 2 and3 are graphical representations useful in explaining the same.

In Fig. 1, I have shown a discharge device comprising a sealed transparent envelope l0 which tion, I consider hydrogen gas to be a suitable medium although other gases, such as helium and argon may be utilized. A pressure on the order of one atmosphere or above is preferably employed.

Within the envelope, there are provided a pair of spaced conducting elements or rods II and [2 which are respectively adapted to serve as anode and cathode for a discharge through the envelope. These elements may be constituted of a refractory metal such as tungsten, or of a material such as carbon, and are supplied with current through suitable lead-in connections l3 and I4 provided at theextremities of the envelope.

As an energizing means for the device, I provide a constant current circuit of any known type. Such a circuit may include, for instance, a direct current source or battery IS in series with a ballast resistance It. As is well known, if the value of the resistance is very high with respect to that-of the discharge device, the current through the latter may be maintained substantially constant irrespective of variations in the voltage drop across it.

With a proper correlation of the supply, circuit and the constants of the discharge device, the

discharge which occurs through the device may encloses an ionizable medium. In this connectinction between these two discharge states, I do not propose herein to attempt any precise definition of them. It is sufllcient to say that two distinguishable states do exist, that they are quite sharply differentiated in character, and that one may exist to the substantial exclusion of the other. It is found that the existence of an arc" or low voltage discharge between thermionically emissive electrodes depends. in large part upon the occurrence. of substantial emission from the cathode electrode by virtue of its temperature, while in the glow or high voltage discharge electrons are produced mainly by positive ion bombardment of the cathode, which may be relatively cold.. A glow discharge involves a voltage drop from two to four times higher than is present in an arc discharge at the same current value.

The foregoing statements are substantiated by studies which I have made of the possible stationary or stable states which may characterize a discharge through a gas at high pressure. Some of these states are shown in Fig. 2 which illustrates the voltage-current characteristic of a device like that of Fig. 1. The full line curves represent respectively the voltage between the terminals of the discharge as a function .of the current for a stable arc state A and for a stable glow state B. Between these two stable states are quasi-stable glow states C and D.

Under certain conditions of current supply and temperature the device may be made to operate on the curve A. However, as the current is decreased the operation may shift suddenly to the second state C, then to the third state D, and finally to the glow state B. The device will then operate stably in the glow state until some further substantial change in conditions occurs which can induce a return to the arc state.

This shift from one operating condition to another may be effected in other ways than by varying the discharge current. Thus, assuming a constant current source, such as is shownin Fig. 1, and further, assuming initial operation in the glow state, substantial heating of the elec trodes will occur. If the discharge current is properly correlated to the heat dissipating capacity of the electrodes (as may readily be assured by proper adjustment of the circuit elements), this heating may be suflicient to cause appreciable thermionic emission from the cathode. When the emission becomes sufiicient, the discharge will transfer more or less abruptly to the are state. Since the voltage drop which corresponds to this state is low, the losses in the distemperature consequently decreases. Finally, a

point is reached at which thermionic emission becomes insufl'icient to sustain the arc discharge and a return to the glow state occurs.

The nature of this transition from one state to another is indicated in Fig. 3, which is based on an oscillographic record of the operation of a device and circuit similar to those of Fig. 1. The discontinuous curves at the top of the figure represent the variations of voltage 6 observed across the discharge device, these being measured with respect to a fixed reference line F. Similarly, the wavy curve next to the bottom represents the variations of current 1' through the device as measured with respect to a fixed reference line H. It will be seen that the current remains substantially fixed as a result of the use of a constant current supply circuit. The voltage, on the other hand, shifts continually from a high value corresponding to a glow state to a low value corresponding to a state of arc discharge. In the particular case studied this change took place with a periodicity of about one cycle per second.

When this discharge takes place in a gas such as hydrogen, the light output of the device depends primarily upon the electrode temperature. Since this varies in turn with the losses in the discharge, it will be seen that with a pulsatory discharge, such as is described in the foregoing, the luminosity will vary in a cyclical fashion. Assuming that the heat input during the glow discharge is suflicient to maintain a condition of high luminosity, while that during the are discharge is insufiicient for this purpose, an off and on effect may be obtained, wherein periods of extremely high luminosity are alternated with periods of low or negligible luminosity. A device having these characteristics is considered to be useful for spectacular or display purposes or in connection with advertising displays, beacons and the like. It has the obvious advantage of requiring no moving parts or switching elements.

It is obvious that the precise operating conditions required to give the effects described I above will vary materially with the design of the discharge device. It is necessary, of course, that the current input be properly correlated with the heat dissipating capacity of the electrode structure to give the desired results. In a particular case, using tungsten electrodes of V diameter and a spacing of about .04", a current of about 1.2 amperes has been found appropriate. This refers to the case in which hydrogen at about 1 atmosphere pressure was employed. For this case, the arc voltage was approximately 200 volts and the glow voltage approximately 400 volts. For other electrode sizes, other values will apply.

While I have described my invention in connection with a particular physical embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. 1, therefore, aim in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A pulsatory light source comprising an envelope enclosing an ionizable medium, a pair of conducting elements within the envelope adapted to serve respectively as anode and cathode, and circuit means for producing a constant current discharge between the conducting elements, the current supplied to the discharge being of such magnitude as to be capable of heating the cathode element to a temperature of efiective thermionic emission during the occurrence of a glow discharge and incapable of maintaining such emission during the occurrence of an arc discharge, whereby the discharge is caused to oscillate between an arc and a glow state.

2. A pulsatory light source comprising cooperative electrodes consisting of spaced tungsten members, an ionizable medium comprising hydrogen at a substantial pressure surrounding the electrodes, and means for supplying substantially constant unidirectional current to the electrodes of sufiicient magnitude with relation to the heatdissipating capacity of the electrodes to cause recurrent transition of a discharge between them from an arc to a glow state, whereby variations in light emission are produced.

3. In the operation of a discharge device of the type which includes spaced solid electrodes and an ionizable medium surrounding the electrodes, the method which comprises supplying to the device constant unidirectional current of such magnitude with relation to the heat dissipating capacity of the electrodes as to produce a discharge which oscillates between a glow and an are state.

CHAUNCEY G. SUITS. 

